- Anna RITZ ZWILLING : Partition function for string-net models
Doctorante en 1ère année, sous la supervision de Jean-Noël Fuchs et Julien Vidal
The discovery of the fractional quantum Hall effect brought into light a new realm of phases of matter, called topologically-ordered phases. In two dimensions, these phases are characterized by exotic emergent excitations, known as anyons, with fractional quantum numbers and anyonic exchange statistics (i.e. neither bosonic nor fermionic). Another fundamental property of topologically-ordered phases is that the ground-state degeneracy depends on the surface topology (i.e. whether the system resides on a sphere, a torus, a pretzel...). The robustness of this degeneracy against local perturbations makes these systems promising candidates for topological quantum computation. Motivated by the latter, recent work has been dedicated to studying the fate of topological order at finite temperature.
In this talk, I will introduce a prominent exactly solvable toy-model for topologically-ordered phases, called string-net model, and present the calculation of its partition function.
- Jérémie KLINGER : Splitting Probabilities of Jump Processes
Doctorant en 3ème année, sous la supervision d'Olivier Bénichou
We derive a universal asymptotic form of the splitting probability of symmetric jump processes which quantifies the probability that the process crosses x before 0 starting from a given position 0 <= x0 <= x. Due to the discrete nature of the process, we show that this probability is non vanishing for the initial condition x0 = 0 and proves to be particularly relevant in applications to light scattering in heterogeneous media in realistic 3D slab geometries.
- Brieuc BENVEGNEN : Flocking in one dimension
Doctorant en 3ème année, sous la supervision d'Alexandre Solon
We study flocking in 1d using the active Ising model, a stochastic lattice gas in which particles self-propel in the direction controlled by the Ising spin they carry. Contrary to the passive Ising model, we observe an ordered phase where particles aggregate and move collectively. Symmetry is not broken though because the aggregate reverses stochastically its direction of motion due to the prominent effect of fluctuations. I will rationalize this behavior by explaining the dynamics of the aggregates and their reversals. At lower temperature, we observe static asters which are amenable to an analytic treatment.
- Léo REGNIER : Complete visitation statistics of one-dimensional random walks
Doctorant en 2ème année, sous la supervision d'Olivier Bénichou
- Adriano ANGELONE : Disorder-free quantum glasses in quasicrystalline lattices
Post-doctorant
Quasicrystals, ordered but not periodic structures, have been originally discovered in the context of solid state physics, and have since inspired considerable research efforts thanks to their peculiar geometric properties. Their experimental realization in photonic systems and cold atom setups has generated further interest, resulting in many studies investigating the properties of interacting quantum particles moving in quasicrystalline lattice structures. One of the most interesting results of these works has been the discovery of Bose Glass (BG) states, globally localized but displaying local patches of delocalized particles. In all of these studies, however, the quasicrystalline substrates were accompanied by disorder, to closely model cold atom experimental platforms; this leaves open the question as to if and how the typical phase diagram of these systems changes in the disorder-free case.
In this talk, I will discuss recent results by my co-workers and I on a system of particles interacting via finite-range interactions on a disorder-free quasicrystalline lattice. Using numerically exact Path Integral Monte Carlo simulations, we obtain the first approximation-free phase diagram of a model in this setting, confirming the existence of a BG phase in the absence of disorder (at odds with previous mean-field predictions). Our results are of great interest given the perspective of laboratory engineering of disorder-free quasicrystalline systems via photonic experiments.
X-ACCESS:1 X-HITS:2352 X-COLOR:598bff X-SHOW-END-TIME:1 END:VEVENT BEGIN:VEVENT DTSTART;TZID=Europe/Paris:20230116T114500 DTEND;TZID=Europe/Paris:20230116T124500 UID:5A60A5AB-1C19-4274-B0AD-927BFAE5BB21 SUMMARY:Louise DELZESCAUX & Pierre RIZKALLAH CREATED:20240207T084533Z DTSTAMP:20240207T084533Z URL:https://www.lptmc.jussieu.fr/vie-scientifique/seminaires-jeunes/louise-delzescaux-pierre-rizkallah DESCRIPTION:- Louise DELZESCAUX : Nonperturbative renormalization group approach to flat polymerized membrane bilayers Doctorante en 2ème année, sous la supervision de Dominique Mouhanna\NPhase transition is a key concept in physics. It is a physical process of transition between two states of a system, induced by a parameter which can be the temperature, a magnetic field, etc. This phenomenon is present in different areas of physics such as condensed matter or particle physics. The Mermin-Wagner Theorem states that there is no symmetry breaking in continuous system with short-range interactions of dimension equal or less than 2. However, polymerized membranes are 2d systems that display a crumpling transition between a high-temperature, crumpled, phase and a low temperature, flat, phase. In this seminar, I will talk about the flat phase of polymerized membranes - which, for instance, is relevant for graphene - and present briefly the renormalization group, the technique we use to study the fluctuations and the behavior of this phase. I will also introduce polymerized membrane bilayers, which is the system I am working on with Dominique Mouhanna for my Phd.\N- Pierre RIZKALLAH : Microscopic models and hydrodynamic description for single-file diffusion\NThe situation where an active particle (called a tracer) diffuses in a complex environment arises in many biological systems (molecular motors, bacteria, micro-swimmers, algae...), but also in soft matter experiments with active colloids. When particles are confined in a one dimensional geometry like pores or narrow channels, the situation is called single-file diffusion because particles cannot bypass each other.This strong geometrical constraint leads to an anomalous scaling ∼ √t for the mean and variance of the displacement of a driven tracer particle. Many microscopic models have been considered to describe this situation. We focus first on the paradigmatic simple exclusion process with a symmetric tracer and its description in terms of fluctuating hydrodynamics. We explain how we can obtain an exact expression for the tracer’s cumulant generating function and its correlations with its environment [1]. Then, we show how the hydrodynamic description can be adapted to describe single-file diffusion with a biased tracer. [2]\N[1] Exact closure and solution for spatial correlations in single-file diffusion. A. Grabsch, A. Poncet, P. Rizkallah, P. Illien, O. BénichouScience Advances 8, eabm5043 (2022)[2] Driven tracer in the Symmetric Exclusion Process: linear response and beyond. A. Grabsch, P. Rizkallah, P. Illien, O. BénichouarXiv:2207.13079. (accepted in Phys. Rev. Lett.) X-ALT-DESC;FMTTYPE=text/html:
- Louise DELZESCAUX : Nonperturbative renormalization group approach to flat polymerized membrane bilayers
Doctorante en 2ème année, sous la supervision de Dominique Mouhanna
Phase transition is a key concept in physics. It is a physical process of transition between two states of a system, induced by a parameter which can be the temperature, a magnetic field, etc. This phenomenon is present in different areas of physics such as condensed matter or particle physics. The Mermin-Wagner Theorem states that there is no symmetry breaking in continuous system with short-range interactions of dimension equal or less than 2. However, polymerized membranes are 2d systems that display a crumpling transition between a high-temperature, crumpled, phase and a low temperature, flat, phase. In this seminar, I will talk about the flat phase of polymerized membranes - which, for instance, is relevant for graphene - and present briefly the renormalization group, the technique we use to study the fluctuations and the behavior of this phase. I will also introduce polymerized membrane bilayers, which is the system I am working on with Dominique Mouhanna for my Phd.
- Pierre RIZKALLAH : Microscopic models and hydrodynamic description for single-file diffusion
The situation where an active particle (called a tracer) diffuses in a complex environment arises in many biological systems (molecular motors, bacteria, micro-swimmers, algae...), but also in soft matter experiments with active colloids. When particles are confined in a one dimensional geometry like pores or narrow channels, the situation is called single-file diffusion because particles cannot bypass each other.
This strong geometrical constraint leads to an anomalous scaling ∼ √t for the mean and variance of the displacement of a driven tracer particle. Many microscopic models have been considered to describe this situation. We focus first on the paradigmatic simple exclusion process with a symmetric tracer and its description in terms of fluctuating hydrodynamics. We explain how we can obtain an exact expression for the tracer’s cumulant generating function and its correlations with its environment [1]. Then, we show how the hydrodynamic description can be adapted to describe single-file diffusion with a biased tracer. [2]
[1] Exact closure and solution for spatial correlations in single-file diffusion. A. Grabsch, A. Poncet, P. Rizkallah, P. Illien, O. Bénichou
Science Advances 8, eabm5043 (2022)
[2] Driven tracer in the Symmetric Exclusion Process: linear response and beyond. A. Grabsch, P. Rizkallah, P. Illien, O. Bénichou
arXiv:2207.13079. (accepted in Phys. Rev. Lett.)
- Timothy FOLDES : Exploring the Coil-Globule Phase Transition: Spectral Analysis, Dynamical Characterization, and application to chromatin modelling.
Doctorant, sour la supervision de Maria Barbi
This presentation focuses on the fundamental phenomenon of the coil-globule phase transition in polymer physics and its role in understanding the structure an its role in understanding the structure and function of biological macromolecules. We first explore the application of spectral analysis to study the equilibrium polymer behavior across the coil-globule transition. We then investigate the dynamics of the polymer and aim to characterize the different phases involved. Finally, we delve into the applications to the modeling of chromatin, the complex of DNA and proteins that forms the chromosomes in eukaryotic cells.
- David ALSPAUGH : Local density of state oscillations in laterally heterostructured topological insulator-semiconductor systems
Post-doctorant
We study local density of state (LDOS) oscillations arising from the scattering of electrons at atomic edge defects in topological insulator (TI) surfaces. To create edge scattering on the surface of a TI, we assume that half of its surface is covered with a semiconductor. In addition to modifying the TI states in the covered half, the presence of the semiconductor leads to a localized edge potential at the vacuum-semiconductor boundary. We study the induced LDOS by imposing time-reversal (TR) invariance and current conservation across the boundary. Additionally, we explore how the scattering of TI junctions with dissimilar spin textures and anisotropic Fermi velocities affect the modulations of the LDOS away from the junction edge. In all cases, for energies close to the Dirac point, we find that the decay envelope of the LDOS oscillations is insensitive to the scattering at the atomic edge defect, with a decay power given by $x^{-3/2}$. Quantitative differences in the amplitude of these oscillations depend on the details of the interface and the spin textures, while the period of the oscillations is defined by the size of the Fermi surface.
LAST-MODIFIED:20240220T152238Z SEQUENCE:1147287 X-ACCESS:1 X-HITS:2508 X-COLOR:598bff X-SHOW-END-TIME:1 END:VEVENT BEGIN:VEVENT DTSTART;TZID=Europe/Paris:20240422T104500 DTEND;TZID=Europe/Paris:20240422T114500 UID:B15966DD-0AB4-4548-890E-71602EF62162 SUMMARY:Léo REGNIER & Anna RITZ ZWILLING CREATED:20240215T154442Z DTSTAMP:20240215T154442Z URL:https://www.lptmc.jussieu.fr/vie-scientifique/seminaires-jeunes/tba DESCRIPTION:- Léo REGNIER : Starving Random Walks Doctorant en 3ème année, sous la supervision d'Olivier Bénichou\NHow long does it take for a tracer to reach a position it has never visited before [1]? And when will a forager starve to death, depending on the medium it moves through or its walking behavior [2]? In this presentation, I will address these two questions. Firstly, I will quantify the exploration dynamics of a memoryless (Markovian) random walk using the time between visits to new sites, which statistics can be separated in three universality classes depending on a few parameters of the walk.Next, I will apply these findings to the foraging random walk problem. Here, the tracer has a finite metabolic time, serving as a minimal model for a depletion-controlled system. In addressing this problem, we will demonstrate how to determine the lifetime, a question that remained elusive prior to this work.\N\N \N[1] Régnier, L., Dolgushev, M., Redner, S. & Bénichou, O., Universal exploration dynamics of random walks. Nat Commun 14, 618 (2023). https://doi.org/10.1038/s41467-023-36233-5\N[2] Régnier, L., Dolgushev, M. & Bénichou, O., From maximum of intervisit times to starving random walks, PRL 132, 127101 (2024). https://doi.org/10.1103/PhysRevLett.132.127101\N \N\N- Anna RITZ ZWILLING : Doctorante en 3ère année, sous la supervision de Jean-Noël Fuchs et Julien Vidal\N X-ALT-DESC;FMTTYPE=text/html:- Léo REGNIER : Starving Random Walks
Doctorant en 3ème année, sous la supervision d'Olivier Bénichou
- Anna RITZ ZWILLING :
Doctorante en 3ère année, sous la supervision de Jean-Noël Fuchs et Julien Vidal
LAST-MODIFIED:20241010T150204Z SEQUENCE:20560642 X-ACCESS:1 X-HITS:2662 X-COLOR:598bff X-SHOW-END-TIME:1 END:VEVENT BEGIN:VEVENT DTSTART;TZID=Europe/Paris:20240603T104500 DTEND;TZID=Europe/Paris:20240603T114500 UID:A9FA521E-1AED-4168-B6DD-EA3FBAA8E68A SUMMARY:Julien BREMONT & Louise DELZESCAUX CREATED:20240215T154531Z DTSTAMP:20240215T154531Z URL:https://www.lptmc.jussieu.fr/vie-scientifique/seminaires-jeunes/tba-2 DESCRIPTION:- Julien BREMONT : Persistence exponents and propagators of self-interacting random walks Doctorant en 2ème année, sous la supervision d'Olivier Bénichou et de Raphael Voituriez\N- Louise DELZESCAUX : Perturbative RG approach to the crumpling transition in disordered polymerized membranes Doctorante en 3ère année, sous la supervision de Dominique Mouhanna X-ALT-DESC;FMTTYPE=text/html:
- Julien BREMONT : Persistence exponents and propagators of self-interacting random walks
Doctorant en 2ème année, sous la supervision d'Olivier Bénichou et de Raphael Voituriez
- Louise DELZESCAUX : Perturbative RG approach to the crumpling transition in disordered polymerized membranes
Doctorante en 3ère année, sous la supervision de Dominique Mouhanna
Salle 523, couloir 12-13, 5è étage
Nicolas Paris : Non-perturbative solution of the three-channel Kondo (3CK) model
In 1964, Kondo explained the resistivity minimum in dilute magnetic alloys as a result of conduction electrons screening localized magnetic moments. This behavior is captured by the simple yet profound Kondo model—a single spin interacting with s-wave conduction electrons—which became a key model in strongly correlated electron physics and was later solved using Wilson’s Numerical Renormalization Group.
In this talk, I will present the three-channel Kondo (3CK) model, where three electron channels compete to screen a single impurity spin. Recently realized experimentally by Iftikhar et al. (Science, 2018), the 3CK model provides a minimal setting to explore quantum criticality and non-Fermi liquid behavior. I will show how the Non-Perturbative Functional Renormalization Group offers valuable theoretical insight into this rich and unconventional physics.
Sankarshan Sahu : Towards a generalization of the Central Limit Theorem to critical systems
The Central Limit Theorem does not hold for strongly correlated stochastic variables, as is the case for statistical systems close to criticality. Recently, the calculation of the probability distribution function (PDF) of the magnetization mode at criticality has been performed with the functional renormalization group in the case of the three-dimensional Ising model. It has been shown that there exists an entire family of universal PDFs parameterized by $\zeta=\lim_{L,\xi_\infty\rightarrow\infty}L/\xi_\infty$ which is the ratio of the system size $L$ to the bulk correlation length $\xi_{\infty}$ with $L,\xi_{\infty}\to\infty$. We compute the whole family of these universal PDFs at both one and two loop orders in perturbation theory and show that the agreement with Monte-Carlo simulations becomes quantitative at two loops.
LAST-MODIFIED:20250618T131332Z SEQUENCE:7770513 X-ACCESS:1 X-HITS:1583 X-COLOR:598bff X-SHOW-END-TIME:1 END:VEVENT BEGIN:VEVENT DTSTART;TZID=Europe/Paris:20250610T104500 DTEND;TZID=Europe/Paris:20250610T114500 UID:C5EBE3B5-8DB1-4D3F-9D52-C678A9A2D4A9 SUMMARY:Vincent Grison & Louis-Martin Poitras CREATED:20250328T075420Z DTSTAMP:20250328T075420Z URL:https://www.lptmc.jussieu.fr/vie-scientifique/seminaires-jeunes/vincent-grison DESCRIPTION:Vincent Grison : Finite-temperature localization transition in a 1D disordered Bose gas : from Normal Fluid to Bose Glass, and more\NThe question of the effects of disorder on phases and phase transitions in quantum systems is a notoriously difficult problem in condensed matter - disordered bosons being a typical example.Following previous works, we use bosonization, the replica method and the Functional Renormalization Group to determine the phase diagram of a one-dimensional disordered Bose gas at finite temperatures.Our study suggests the existence of a thermal phase transition between a low-temperature many-body localized phase and a high-temperature normal fluid phase, in qualitative agreement with an earlier proposal.We also uncover the existence of an intermediate glassy regime just above the transition temperature, controlling the behavior of the system on a significant range of length and time scales.\NLouis-Martin Poitras : New generalized force-field for sulfide glasses and crystals\NWe present a generalized Born-Mayer force-field for modeling sulfide glasses and crystals relevant to all-solid-state batteries. The force-field captures key structural features, including sulfur-bridged tetrahedra and medium-range order, via a combination of two- and three-body terms. Fitted to crystal structures and experimental scattering data, the model reproduces the essential properties of the glassy and crystalline state. By accurately reproducing realistic structures across a range of sulfide compositions, the proposed force-field paves the way for investigating mechanical, dynamical and electrical properties of sulfide electrolytes through classical molecular dynamics simulations. X-ALT-DESC;FMTTYPE=text/html:Vincent Grison : Finite-temperature localization transition in a 1D disordered Bose gas : from Normal Fluid to Bose Glass, and more
The question of the effects of disorder on phases and phase transitions in quantum systems is a notoriously difficult problem in condensed matter - disordered bosons being a typical example.
Following previous works, we use bosonization, the replica method and the Functional Renormalization Group to determine the phase diagram of a one-dimensional disordered Bose gas at finite temperatures.
Our study suggests the existence of a thermal phase transition between a low-temperature many-body localized phase and a high-temperature normal fluid phase, in qualitative agreement with an earlier proposal.
We also uncover the existence of an intermediate glassy regime just above the transition temperature, controlling the behavior of the system on a significant range of length and time scales.
Louis-Martin Poitras : New generalized force-field for sulfide glasses and crystals
We present a generalized Born-Mayer force-field for modeling sulfide glasses and crystals relevant to all-solid-state batteries. The force-field captures key structural features, including sulfur-bridged tetrahedra and medium-range order, via a combination of two- and three-body terms. Fitted to crystal structures and experimental scattering data, the model reproduces the essential properties of the glassy and crystalline state. By accurately reproducing realistic structures across a range of sulfide compositions, the proposed force-field paves the way for investigating mechanical, dynamical and electrical properties of sulfide electrolytes through classical molecular dynamics simulations.
LAST-MODIFIED:20250618T131305Z SEQUENCE:7103925 X-ACCESS:1 X-HITS:1343 X-COLOR:598bff X-SHOW-END-TIME:1 END:VEVENT BEGIN:VEVENT DTSTART;TZID=Europe/Paris:20260602T104500 DTEND;TZID=Europe/Paris:20260602T114500 UID:06212F2D-F193-413A-B8D7-91E6ECDE3ACE SUMMARY:Elia Bronzo & Arthur Plaud CREATED:20260331T131253Z DTSTAMP:20260331T131253Z URL:https://www.lptmc.jussieu.fr/vie-scientifique/seminaires-jeunes/2026-06-02-08-45-00 DESCRIPTION:- Elia Bronzo :\N \N- Arthur Plaud :\N X-ALT-DESC;FMTTYPE=text/html:- Elia Bronzo :
- Arthur Plaud :
LAST-MODIFIED:20260414T122421Z SEQUENCE:1206688 LOCATION: GEO:0.00000000;0.00000000 X-LOCATION-DISPLAYNAME:Salle 523, couloir 12-13, 5è étage X-ACCESS:1 X-HITS:2 X-COLOR:598bff X-SHOW-END-TIME:1 END:VEVENT BEGIN:VEVENT DTSTART;TZID=Europe/Paris:20260623T104500 DTEND;TZID=Europe/Paris:20260623T114500 UID:18FC134B-D137-4D92-A49B-5798A4625D35 SUMMARY:Dafne Prado & Pierre-Louis Taillat CREATED:20260331T131326Z DTSTAMP:20260331T131326Z URL:https://www.lptmc.jussieu.fr/vie-scientifique/seminaires-jeunes/2026-06-23-08-45-00 DESCRIPTION:- Dafne Prado : \N \N- Pierre-Louis Taillat :\N X-ALT-DESC;FMTTYPE=text/html:
- Dafne Prado :
- Pierre-Louis Taillat :
LAST-MODIFIED:20260414T122038Z SEQUENCE:1206432 LOCATION: GEO:0.00000000;0.00000000 X-LOCATION-DISPLAYNAME:Salle 523, couloir 12-13, 5è étage X-ACCESS:1 X-HITS:1 X-COLOR:598bff X-SHOW-END-TIME:1 END:VEVENT END:VCALENDAR